This invention relates to an internal combustion engine and more particularly to an improved induction system for such engines and particularly those having multiple intake valves.
It has been acknowledged that the performance of an internal combustion engine can be substantially improved by providing multiple intake valves. By employing a larger number of smaller valves having the same effective flow area, the breathing capacity of an engine can be improved and the performance improved. This is primarily due to the better distribution of the flow area and also the lower inertia of the valve components. Single large valves are quite heavy and require large return springs that add to the mechanical losses in the engine.
One disadvantage with the increased induction capability, however, is that the engine performance tends to deteriorate at lower speeds and lower loads. The reason for this has been found to be that the air velocity in the combustion chamber is quite low at low speeds and this results in reduced combustion rates due to the slow flame propagation. As a result, in conventional multi-valve engines, the engine tends to run inefficiently at low speeds.
There have been proposed, therefore, induction systems wherein the effective flow area of the intake passage is varied so as to provide high breathing capabilities at high speeds and high loads. However, the area of the induction passage is effectively reduced at low speeds and low loads so as to maintain higher flow velocities and improved turbulence in the combustion chamber.
In addition to the desirability of maintaining good combustion conditions and high power outputs, there is also the question of emission control. At times, engines which have efficient intake passages may produce high amounts of unwanted exhaust gas constituents and, particularly, NO.sub.x. It has been proposed to limit or reduce the amount of NO.sub.x emissions by lowering the combustion temperature. One way in which this can be done is by introducing exhaust gases into the intake system. This practice called "EGR" is utilized in many engines.
However, the tolerance of the engine to exhaust gas recirculation is limited. That is, with most engines there is a practical limit as to the amount of exhaust gases which can be recirculated. If this limit is exceeded, then very rough running engine performance results.
It is, therefore, a principal object of this invention to provide an improved engine induction system which permits performance gains throughout the entire power band and which also permits the use of high amounts of exhaust gas recirculation for emission control.
It is a further object of this invention to provide an improved induction system for an engine wherein high amounts of exhaust gas recirculation can be obtained without reducing engine performance or introducing rough running.
It should be obvious from the foregoing description that multi-valve engines having the form of induction control that varies the effective are of the intake passages can become quite complicated. This presents problems, particularly with automotive applications because of the limited available space.
It is, therefore, a still further object of this invention to provide an improved induction system for an engine which provides adequate and the desired air flows under all running conditions and wherein the induction system is nevertheless compact and efficient.
One of the ways in which a multi-valve engine can be configured so as to provide a smaller effective flow area at lower speeds is through the use of throttle valves in one or more of the intake passages. By throttling the flow through certain of the intake passages, the flow velocity through the remaining intake passages can be increased. It also has been the practice to provide a control valve for the engine intake passage wherein the control valve, in addition to restricting the flow, can redirect the flow.
It has been found that tumble, a type of swirling motion that occurs about a transverse axis to the cylinder bore axis, can significantly improve engine running under certain load conditions. One of the advantages of tumble is that the tumble action continues to increase as the piston approaches it top dead center position. More conventional swirl around the cylinder bore axis may tend to diminish as the piston reaches top dead center condition. The time when the turbulence is desirable to improve combustion is at the time of firing of the spark plug which is close to top dead center position. Therefore, tumble has some advantages over swirl.
Tumble, on the other hand, is more difficult to generate in the combustion chamber. This is particularly true when multiple valves are employed. Particularly, when three intake valves are utilized per cylinder, then the flow from the center intake valve tends to create a tumble motion in an opposition to that of the side intake valves.
In order to generate tumble, therefore, control valve arrangements have been proposed which will redirect the flow through at least certain of the valve seats. Therefore, it should be apparent from the foregoing description that the use of multiple intake passages dictates, with most prior art type of constructions, rather complicated valve arrangements.
It is, therefore, a still further objection of this invention to provide a simplified control valve arrangement for a multi-valve engine.
The use of fuel injection systems for engines has also been resorted to as a way of improving engine performance and, at the same time, obtaining emission control and fuel economy. Fuel injectors offer the possibility of providing better control over the amount of fuel inducted into the engine and also can afford advantages in obtaining stratification relative to carbureted engines.
However, fuel injectors tend to be more expensive and require sophisticated control systems. Therefore, it is desirable, even with multiple valve engines, to employ a lesser number of fuel injectors than the actual number of intake ports or intake valves in the engine. Where multiple ports are utilized and the flow through the ports is controlled so that the flow is not uniform under some running conditions, then fuel distribution can become a problem.
It is, therefore, a still further object of this invention to provide an improved induction and fuel injection system for multiple valve engines.
It is a yet further object of this invention to provide an improved fuel injection system for a multi-valve engine wherein a single fuel injection may be utilized and the desired degree of fuel distribution under all running conditions can be obtained.
Because of the added costs penalties of direct cylinder injection, it has been the practice employ manifold fuel injected systems. These systems, however, are more likely to suffer from distribution problems as aforenoted. It is, therefore, a still further object of this invention to provide an improved single injector manifold injection systems for a multi-valve engine.
As is well known, fuel injectors generally inject the fuel into the airstream at a relatively high velocity. High injection pressures are desirable in order to ensure that the fuel is adequately vaporized or atomized when it enters the flowing airstream. However, the orientation of conventional intake passages requires the positioning of the fuel injector in an orientation so that its spray axis is directed transversely to the flow axis through the intake passage. As a result, there is a likelihood with conventional systems of having the fuel actually deposit on the opposite side of the intake passage from where it is injected. This gives rise to obvious problems.
It is, therefore, a still further object of this invention to provide an improved induction system that permits the fuel to be injected in a direction generally along the flow axis in the intake system.